Visible Light Detector B

Transcription

1 Over 150 million die shipped per year DESCRIPTION The is a low cost visible light sensor, with a current output which is directly proportional to the light level. It has a built in optical filter to provide a response which is close to the human eye, or photopic. The output current can be converted to a voltage by connecting it in series with a resistor. The dynamic range is determined by the external resistor and power supply (10K and 5V gives a range of 0 to 160 Lux, but can be over 700 Lux with a 1K resistor). The internal dark current cancellation enables high accuracy over the full temperature range, even at low light levels. FEATURES Near human eye photopic response High IR rejection integrated optical filter Current output highly linear vs light level Temperature stable Integrated high gain photocurrent amplifier Darkcurrent cancellation APPLICATIONS Dawn/dusk sensing Security lighting Display backlighting in laptops, mobile phones, LCD TVs Nightlights 1.0 BASIC APPLICATION & TEST CIRCUIT Figure 1 Vdd Rss Vss Pin Description Vdd Positive terminal Vss Negative terminal Page 1 of 16 This document is the property of Semefab Ltd and is furnished in confidence and upon the condition that it is neither copied nor released to a third party without prior consent.

2 2.0 ABSOLUTE MAXIMUM RATINGS PARAMETER RATING UNITS Supply input voltage 0.3 to 10 V Supply current Internally limited ma Operating Temperature, T O 40 C to 85 C * C Storage Temperature, T S 40 C to 100 C C * The light sensor will function up to 105 C but dark current will have to be taken into consideration. Note that dark current doubles every 10 C. 3.0 ELECTRICAL SPECIFICATION The following parameters apply over the operating temperature range 40 o C to 85 C, and with Rss=10 KOhms and Vdd= 5V, as per figure 1. The is available in 3 variants determined by the tolerance of their output current. The table below shows the range of output currents, for specific lighting conditions, for each variant. Parameter Symbol Test Conditions Min Typ Max Units Infra red response 900 nm % of peak Min. operating voltage V DD V SS Iss =250 Iss = V V Output Current / 15% I SS 200 Lux 100 Lux 10 Lux / 25% I SS 200 Lux 100 Lux 10 Lux / 40% I SS 200 Lux 100 Lux 10 Lux Dark Current I DRK 0 Lux, Ta = 25 C 0 Lux, Ta = 85 C na na Gain Linearity % Peak Spectral 520 nm Response Sensitive Area mm 2 Useable light range R SS & V DD dependant Lux Note that with a lower Rss resistance, the linear light response range can be greatly increased. See section 3.1. Page 2 of 16

3 Vss (V) 3.1 Selection of Rss The can be used over a range of lighting conditions by selecting a suitable value of Rss (see figure 1), or by varying Vdd. Also, there is a lower gain version of this device available, the , which is designed to work at higher light levels. This table summarises how to select values of Rss, and shows which device ( or ) is suitable for each desired application. The graph below also illustrates the usable ranges of both the and , with 1K, 10K and 25K resistors. Note that for these examples Vdd is fixed at 5V. (There is also a E version which has typical response of 100uA at 100 Lux). Light Range to 80 Lux 25K 0 to 160 Lux 10K 0 to 750 Lux 1K 25 K 0 to 1700 Lux 10 K 0 to 6000 Lux 1 K 4 Vss versus Lux Typical values Vdd = 5V Comparison between and with Rss = 25k with Rss = 10k with Rss = 1k with Rss = 25k with Rss = 10k with Rss = 1k LUX Page 3 of 16

4 Relative Response (%) 3.2 Characteristic Curves 100% 90% Photopic Response vs wavelength 80% 70% 60% 50% 40% 30% 20% 10% 0% Wavelength (nm) Rss= 25KOhms Rss= 10KOhms Rss= 1KOhms Page 4 of 16

5 leakage (na) Vss (Volts) Vss vs Temperature 5 Volts & 5 Lux, Rss = 10k 5 Volts & 50 Lux, Rss = 10k Temperature (C) Dark Leakage vs Temperature Temp (C) Page 5 of 16

6 4.0 Application Examples Automatic Night Light Fig 2 This circuit shows the in an Automatic Night Light application. Live Small Light Bulb 220VAC 3.9M SCR YDA01 Note 1 Neutral Fig 2 Note 1 This circuit requires a sensitive gate SCR, with igt(typ) less than 10 The Lamp current is switched by a sensitive gate SCR. The typical gate current of the SCR should be less than 10. When the light is above threshold, current flows between the Vdd and Vss pins of the ASIC which diverts current away from the gate of the SCR. The light switching threshold can be adjusted by choosing different values for and. Page 6 of 16

7 LED Drivers Fig 3 is a very simple low cost circuit using the to switch an LED. 82k 220R T BC550C LED Fig 3 As the light increases, current flows between the Vdd and Vss pins of the ASIC which pulls down the base of T. In dark conditions supplies current to the base of T to switch on the LED. The base current of T must be small compared to the photo current. This circuit should only be used when the current in the LED is less than 10mA. The DC current gain (hfe) of T should be > 400 to minimise the base current. The BC550C or equivalent is a suitable transistor for T. This circuit is not suitable for < 4V because of the headroom required for the LED and T. should be adjusted by customers to obtain the switching threshold to suit the application. This circuit does not have a sharp switching threshold. The LED brightness decreases over a range of about 30 Lux as the ambient light level increases towards the cutoff point. The LED current will switch off completely when is pulled down below about 2.5V. The advantage of this circuit is that it has the smallest number of components. Page 7 of 16

8 Fig 4 is a general purpose LED driver. 47k LED R4 220R 27k 10K T BC550C T BC550C Fig 4 The LED switches ON when the light is less than the switching threshold (Slux). The base current of T will affect the switching threshold. To minimise this effect the base current into T should be less than 10 under all conditions of temperature and supply voltage. When the ambient light >Slux T pulls down and switches off T. For battery operated applications low current drain is important and the value of should be as high as possible so that when the LED is off the circuit quiescent current is low. Slux is controlled by and the base emitter voltage of T. limits the base current into T to prevent excess current with high illumination. R4 controls the LED current. Fig 5 In this circuit the LED switches ON when the light is above the switching threshold Slux. 27k 10K 10k 100k T BC557A LED R5 220R T 9014 Fig 5 The value of in this circuit can be lower than that in Figure 4 because the current in T is switched off in low light conditions. Page 8 of 16

9 Relay Drivers Fig 6 The relay coil is energised when the light < Slux. 27k 10k 10k T BC550C D1 1N4148 T A B Fig 6 The Slux threshold is set by in the same way as explained in the description for circuit figure 5. For battery operated circuits, the hfe of T should be high to allow a high value for. The hfe of T should be high so that a low base current will be able to pull down. Example: = 6V, relay coil resistance = 100R. Min hfe of T = 100, min hfe of T = 200 Coil current = 56mA. Min base current to switch on T = 0.56mA. so = 10K. Min base current of T = 0.56mA/200 = 2.8. With the above value for, the quiescent current when the relay is off would be around 0.6mA which might be too high for some battery operated circuits. Page 9 of 16

10 Fig 7 The relay coil is energised when light > Slux. 27k T D1 1N4148 A 10k 10k R4 100k T B Fig 7 In this case the quiescent current is low in dark conditions because T is switched OFF at the same time as T and the relay coil. The customer can control the current to the application and the quiescent current by choosing a normally open (NO) or normally closed (NC) relay. Interface Circuit Examples Fig 8 shows an interface to a microprocessor. 10k Microprocessor A/D Fig 8 The voltage across varies linearly with the illumination of the sensor. The current between the Vdd and Vss pins is approximately 1.25/lux, so with a 10K resistor the voltage at the A/D input will be 12.5mV per lux. The was designed for low lux applications and the headroom required between Vdd and Vss becomes a problem at higher lux levels. These parts are not ideally suited to control room lighting applications especially if the microprocessor supply voltage is low. For higher lighting applications such as the control of Page 10 of 16

11 room ambient lighting or backlighting applications for TVs, computers or mobile phones then the should be used (see section 3.1). Fig 9 This circuit uses a transistor to provide a light level switching interface between the and CMOS logic. 27k 10K 100k T 9014 OUT Fig 9 The switching threshold is set by and the base of T as explained for previous circuit examples. The OUT signal will be high when the illumination is above the threshold and low when it is below the threshold. Using a buffer instead of an inverter will change the polarity of the OUT signal Fig 10 This circuit uses a comparator (or opamp) to provide a level switching interface for the. 180k V V OUT 18k 22k Fig 10 OUT will be high when the voltage at Vss < 0.1*Vdd. Page 11 of 16

12 Fig 11 Same as Fig 10 except that OUT will be high when the voltage Vss > 0.1* 180k V V OUT 18k 22k Fig 11 Fig 12 The opamp circuit amplifies the output voltage at Vss. VOUT = (1 /) Iphoto* V V OUT Fig 12 Page 12 of 16

13 5.0 PACKAGING INFORMATION light sensors can be supplied as bare die or packaged. 5.1 LED STYLE PACKAGE (dimensions in mm with ±0.1mm tolerance) Page 13 of 16

14 5.2 SMD STYLE PACKAGE (dimensions in mm with ±0.1mm tolerance) PACKAGE Page 14 of 16

15 5.2.2 REEL PACKING 5 reels per box Page 15 of 16

16 6.0 ORDERING INFORMATION To order or E, please use code in the following table: Options Ordering Code Nominal Response Die Thickness Output Current Tolerance Supply Format 1.25 /Lux 1.0 /Lux E 300 µm G 525 µm NG / 15% 15 / 25% 25 / 40% 40 Bare die, unsawn wafer D1 Bare die, sawn wafer D2 LED style package L Surface mount package S Examples: To order sawn wafers, 300 µm thick, with a tolerance of / 40% and responsivity of 1.25/Lux then use the ordering code: G40D2. To order in a surface mount package with 15% tolerance and responsivity of 1.25/Lux, use ordering code: 15S Note: Surface mount style packages require that the wafer be ground down to 300 µm. For LED style packages, grinding is not required. Therefore in both cases thickness does not need to be specified. Page 16 of 16